Ram usage is really nothing to worry about depending on the amount you have. Windows will free ram where needed as long as there is enough. If ram is not being used by applications it will be used for other things (it will be cached I believe?). If almost no ram is being used it means some things might take longer to load.
Windows on my Surface Go 2 used about 3-4GB of ram when idle, while on my work laptop with 64GB ram it uses about 10-12GB. But if necessary applications can use some of that ram that’s normally being used in idle.
I do agree about Linux distros being faster, that’s my experience as well.
Exactly, most, if not all, os’s do this.